Human Heredity

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Chapter 11

• Human Heredity

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11-1 It runs in the family

• Many characteristics of human children are
  genetically determined
• Many human traits are inherited by the action of
  dominant and recessive allele genes, although
  other traits are determined through more
  complicated gene interactions

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The Human Organism A Review

• Diploid cell 2 sets of homologous chromosomes
• 46 chromosomes
• 23 pairs

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• 6 billion nucleotide pairs
• 3,000 letters to a page over 1 million pages

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• Gametes sperm or egg
• Contain a single copy of a gene

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• Zygote fertilized egg 46 chromosomes
• Formed when sperm and egg unite

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Human Traits

• Phenotype is only partly determined by the
  genotype
• Some traits are strongly influenced by
  environmental factors (non-genetic)
• Examples exercise and nutrition

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• It is important to consider the influence of the
  environment on the expression of some genes, it
  must be understood that environmental effects on
  gene expression are not inherited

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• Genes that are denied a proper environment in
  which to reach full expression in one generation
  can, in a proper environment, achieve full
  potential in a later generation (page 229)

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11-2 The Inheritance of Human Traits

• more than 3,000 human genes have been described

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Human Blood Groups

• Multiple alleles genes with more that two forms
• Example ABO and Rh blood groups
• Remember an organism can have two alleles
  only!

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• Blood Type determined by the presence or
  absence of certain things in the blood
• RBC (Red blood cell) can carry two different
  antigens
• Antigens molecules that can be recognized by
  the immune system

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Genotypes and Phenotypes

• ii
• IAIA or IAi
• IBIB or IBi
• IAIB

• Type O
• Type A
• Type B
• Type AB

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Rh Blood Groups

• Rh antigen also on RBC
• Rh - have antigen (Dominant)
• Rh_ - no antigen (Recessive)

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Huntingtons Disease

• Caused by a single Dominant allele
• Appears in 30s or 40s
• Progressive loss of muscle control and mental
  function ? death
• Gene on chromosome 4

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Sickle Cell Anemia

• Caused by a change in one of the polypeptides
  found in hemoglobin (carries oxygen in RBC)
• One nucleotide difference
• Codominant inheritance pattern HAHS
• HA - normal allele
• HS Sickle Cell allele

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• Sickle Cell Anemia common in people of African
  ancestry and from tropical regions
• Carriers (heterozygous) of Sickle Cell trait
  (HAHS) resistant to malaria

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Polygenic Traits

• Human traits that are controlled by a number of
  genes
• Example Height, Body weight, skin color
• Phenotypes seen in a range

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Example Skin Color

• 4 genes some may have multiple alleles
• Color is determined by the combination of genes
• Melanin dark colored pigment
• The darker you are the more genes you have that
  code for the production of melanin

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11-3 Sex-Linked Inheritance

• Genes on an X chromosome are inherited in a sex
  linked pattern

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Nondisjunction

• Failure of chromosomes to separate properly
  during one of the stages of meiosis
• Turners Syndrome 45X female
• Klinefelters Syndrome 47XXY - male

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• Babies are not born without and X
• X is essential for survival
• Sex is determined by the presence or absence of Y
• Y switches on a male pattern of growth

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Sex-Linked Genetic Disorders

• Gene for the trait is on the X or Y
• X has many genes Y has few
• Defects easy to spot appear more in males

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Colorblindness

• Recessive X linked disorder
• Cannot distinguish colors
• Dominant Gene XC
• Recessive Gene - Xc

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Carrier

• A heterozygous female has the gene but does not
  express it can pass it on to her children

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Hemophilia

• Recessive X linked disorder
• Blood does not clot
• XH good gene
• Xh hemophilia gene

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Muscular Dystrophy

• Results in the progressive wasting away of muscle

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Sex Influenced Traits

• A trait that is caused by a gene whose expression
  differs in males and females

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Baldness

• A sex influenced trait
• Single gene two alleles

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11-4 Diagnosis of Genetic Disorders

• Downs Syndrome Trisomy 21
• Extra copy of the 21st chromosome
• Can be detected by microscopic examinations of
  chromosomes
• karyotype

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Parental Diagnosis

• Amniocentesis removes fluid from the sac around
  the baby
• The fluid can be used to grow cells and make a
  karyotype
• Chorionic Villus Biopsy cells are removed from
  the embryo
• Faster than amnio.

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• CVB and Amnio make it possible to detect
  chromosomal abnormalities
• Test for biochemical abnormalities
• Presence of certain DNA sequences

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• We can detect over 100 disorders
• Knowledge leads to choices and decisions
• Ethical Considerations